The recent drive for higher integration and operating speeds in LSI devices makes it necessary to further reduce the pattern rule. Deep-ultraviolet lithography was developed as an essential technology for micropatterning to a feature size of 0.3 μm or less. Among others, the KrF excimer laser lithography has been fully recognized as a commercial scale production technology.
With respect to chemically amplified resist compositions adapted for the photolithography using ArF excimer laser light of 193 nm wavelength as a light source, the primary requirement is, of course, a high transparency at that wavelength. They are also required to meet a high etch resistance sufficient to comply with film thickness reduction, a high sensitivity sufficient to minimize the burden to expensive optical materials, and among others, a high resolution sufficient to form an exact fine pattern. The key toward these requirements is to develop a base resin featuring high transparency, high rigidity and high reactivity. Active efforts have been devoted for such development.
Typical resins known to be highly transparent to ArF excimer laser light are copolymers of acrylic or methacrylic acid derivatives as disclosed in JP-A H04-39665.
One of the (meth)acrylic resins proposed thus far is a combination of (meth)acrylic units having methyladamantane ester as acid labile group units with (meth)acrylic units having lactone ring ester as adhesive group units as disclosed in JP-A H09-90637. Acid labile groups of exo form are described in U.S. Pat. No. 6,448,420 (JP-A 2000-327633). These groups have so high an acid elimination ability and require a low level of activation energy for acid elimination, affording a high resolution and low dependence on post-exposure bake (PEB). Norbornane lactone is also proposed as an adhesive group having enhanced etching resistance as disclosed in JP-A 2000-26446 and JP-A 2000-159758. These studies have achieved significant improvements in the resolution of ArF resists.
However, in an attempt to form a fine pattern having a pitch of less than 200 nm, prior art resist materials are difficult to form patterns and the patterns, if formed, have insufficient rectangularity and substantial roughness on their surface and sidewalls. They are hardly believed to clear the practically acceptable level. Of the problems associated with prior art resist materials, the most serious problem is the unevenness of fine line size, which is generally referred to as “line edge roughness” (LER). Since the LER has a substantial impact on the performance of semiconductor devices being fabricated, it is strongly desired to overcome this problem. If it is merely desired to form patterns in smooth finish, the purpose may be attained to some extent by using a resin having a relatively low molecular weight or by selecting a photoacid generator capable of generating a rather mobile acid. These attempts, however, substantially sacrifice other properties such as exposure dose dependency, pattern density dependency, and mask fidelity. Additionally, they do not lead to a reduction of LER since a fine fluctuation of a mask is so exaggerated that the line size itself becomes rather uneven. It is desired to have an essential solution to improve LER without degradation of resolution so that the solution may accommodate a further miniaturization of the ArF excimer laser lithography and a higher resolution by virtue of the immersion lithography process.
Citation List
Patent Document 1: JP-A H04-39665
Patent Document 2: JP-A H09-90637
Patent Document 3: U.S. Pat. No. 6,448,420 (JP-A 2000-327633)
Patent Document 4: JP-A 2000-26446
Patent Document 5: JP-A 2000-159758